On the Physical Basis of Asymmetry and Homochirality

Abstract

Mirror symmetry breaking is ubiquitous in our visible universe taking place in elementary particles, atoms, and molecules. Molecular chirality is not biogenic in itself, although its detection is often considered a biosignature, a conjecture inferred from the fact that we do not know life devoid of homochirality. The question of whether there is a connection between the cosmic preference for one enantiomer, as imposed by the weak force, and the single chirality displayed on Earth is vividly debated. This article gives a glimpse on the origin of asymmetry from a cosmological perspective and on physical transformations that lead to an enantiomeric imbalance, leaving chemical reactions essentially aside. These processes are more plausible as sources of prebiotic chirality than asymmetric amplifications requiring unnatural substrates and conditions and fighting against racemization. The latter may actually be a friend, not foe, and a driving force for enantioselection.

Aza[6]helicene Platinum Complexes: Chirality Control of cis–trans Isomerism

“…Pure enantiomers and their racemic mixture are known to display different physical properties such as melting points and solubilities 3. One can take benefit from these different physical properties to optimize, for instance, resolution processes of chiral molecules3 or to perform uncommon reactivity such as amplification processes 4a–d. In the liquid phase, identical physical and chemical properties are generally observed for pure enantiomers and their racemic mixture, except in those cases where strong homochiral and heterochiral associations take place 4e.…”

Molecular Chirality in Meteorites and Interstellar Ices, and the Chirality Experiment on Board the ESA Cometary Rosetta Mission

“…Further investigation of chiral resolution through sublimation and other astrophysically admissible processes may provide new insight on this topic. [67]…”

Hydration of serine–metal cation complexes: implication for the role of water in the origin of homochirality on the Earth

“…The problem of the origin of homochirality in living systems has been widely discussed. There are theories assuming that serine could play an important role in this matter (Ávalos et al 2010;Blackmond and Klussmann 2007;Cintasi and Viedma 2012;Klussmann and Blackmond 2009;Kojo 2010;Ruiz-Mirazo et al 2014;Toxvaerd 2009). The serine role could be related to the following findings: serine exhibits a eutectic point of > 99% enantiomeric excess-ee (Klussmann et al 2006), sublimation of serine with the initial ee of 3% yielded sublimates of 68-92% ee (Perry et al 2007), and under some specific conditions (e.g., electrospray ionization conditions) serine yields stable preferentially homochiral octamer (Cooks et al 2001;Nanita and Cooks 2006), although it has to be added that serine octamer does not exist in solution (Vandenbussche et al 2006).…”